Soil types FAQs

What is meant by soil ‘texture’?

Garden soils contain particles of varying size. Clay particles are minute and tend to clog together (which is why clay is so heavy and difficult to work). At the other end of the scale, gravel consists of very large particles; this type drains very easily and so is known as a hungry soil. Between these two extremes will be found comparatively small soil particles, known as silt, and larger particles of sand. The majority of soils consist of mixtures of the different-sized particles. The proportions of large, medium, and small particles in a given soil determine its texture.

I know that a soil’s quality depends greatly on its structure. What makes for good structure?

A soil has good structure if it contains a balanced range of particle sizes that provide air pockets of a size to accommodate the right amount of air and moisture for healthy plant growth; drains well; and contains adequate humus and organic material. One way of encouraging good soil structure is to incorporate sufficient garden compost and other bulky organic material. Over-cultivation, especially with rotary cultivators, tends to spoil structure.

What is tilth?

When a soil has been forked and raked and its clods have been broken down to a fine, workable texture it is said to have good tilth. This quality is particularly important when small seeds are being sown, because it enables them to make good contact with the available soil moisture. Too fine a texture does not make a good tilth because such a soil’s surface will cake in the first shower of rain. Heavy clay soils are often difficult to rake down to a fine surface because the particles clog together and bake hard in dry weather. Such soils are best dug and left rough in autumn; winter frosts crumble the heavy lumps of soil, which are then much easier to bring to a fine tilth in spring.

What is the difference between clay and silt?

Both are types of soil. Clay consists of particles less than 0.002 mm (0.0001 in) in diameter. It is very sticky when wet, smears, and shines without any feel of grittiness when rubbed between finger and thumb. A clay surface cracks as it dries out and the soil is difficult to manage. Silt particles are slightly larger than those of clay (0.002-0.02 mm), but are equally liable to give a poor-draining soil, although silt’s presence in fast-draining sandy soils can be beneficial. Silt feels smooth and silky when rubbed between finger and thumb. Unfortunately silt particles do not flocculate (join together) to form crumbs when lime is mixed with them as do clay particles.

The first thing to do is to dig one or two holes 1 m (3Vh ft) deep to find out why drainage is poor. A mechanical or mineral pan may thus be fractured—and that would probably solve the problem.

If there is no pan, it may be necessary to lay land drains . Poor surface drainage can sometimes be overcome by simply improving soil tilth.

How can I improve water-retention in a stony soil?

Owing to excessive drainage, stony soils are always hungry: they tend to be warmer, and their humus is burned up very quickly. Dig in well-rotted manure, garden compost, peat, or other bulky organic material to improve retention, while a mulch of the same sort of material will lessen evaporation from the surface.